Add support for composite ids.

Entities may be annotated with `@Id` and `@Embedded`, resulting in a composite id on the database side.
The full embedded entity is considered the id, and therefore the check for determining if an aggregate is considered a new aggregate requiring an insert or an existing one, asking for an update is based on that entity, not its elements.
Most use cases will require a custom `BeforeConvertCallback` to set the id for new aggregate.

For an entity with `@Embedded` id, the back reference used in tables for referenced entities consists of multiple columns, each named by a concatenation of <table-name> + `_` + <column-name>.
E.g. the back reference to a `Person` entity, with a composite id with the properties `firstName` and `lastName` will consist of the two columns `PERSON_FIRST_NAME` and `PERSON_LAST_NAME`.
This holds for directly referenced entities as well as `List`, `Set` and `Map`.

Closes #574
Original pull request #1957

Author: schauder

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/DefaultDataAccessStrategy.java

@@ -117,6 +117,7 @@ public <T> Object insert(T instance, Class<T> domainType, Identifier identifier,
 	public <T> Object[] insert(List<InsertSubject<T>> insertSubjects, Class<T> domainType, IdValueSource idValueSource) {
 
 		Assert.notEmpty(insertSubjects, "Batch insert must contain at least one InsertSubject");
+
 		SqlIdentifierParameterSource[] sqlParameterSources = insertSubjects.stream()
 				.map(insertSubject -> sqlParametersFactory.forInsert( //
 						insertSubject.getInstance(), //
@@ -167,7 +168,7 @@ public <S> boolean updateWithVersion(S instance, Class<S> domainType, Number pre
 	public void delete(Object id, Class<?> domainType) {
 
 		String deleteByIdSql = sql(domainType).getDeleteById();
-		SqlParameterSource parameter = sqlParametersFactory.forQueryById(id, domainType, ID_SQL_PARAMETER);
+		SqlParameterSource parameter = sqlParametersFactory.forQueryById(id, domainType);
 
 		operations.update(deleteByIdSql, parameter);
 	}
@@ -188,7 +189,7 @@ public <T> void deleteWithVersion(Object id, Class<T> domainType, Number previou
 
 		RelationalPersistentEntity<T> persistentEntity = getRequiredPersistentEntity(domainType);
 
-		SqlIdentifierParameterSource parameterSource = sqlParametersFactory.forQueryById(id, domainType, ID_SQL_PARAMETER);
+		SqlIdentifierParameterSource parameterSource = sqlParametersFactory.forQueryById(id, domainType);
 		parameterSource.addValue(VERSION_SQL_PARAMETER, previousVersion);
 		int affectedRows = operations.update(sql(domainType).getDeleteByIdAndVersion(), parameterSource);
 
@@ -208,8 +209,7 @@ public void delete(Object rootId, PersistentPropertyPath<RelationalPersistentPro
 
 		String delete = sql(rootEntity.getType()).createDeleteByPath(propertyPath);
 
-		SqlIdentifierParameterSource parameters = sqlParametersFactory.forQueryById(rootId, rootEntity.getType(),
-				ROOT_ID_PARAMETER);
+		SqlIdentifierParameterSource parameters = sqlParametersFactory.forQueryById(rootId, rootEntity.getType());
 		operations.update(delete, parameters);
 	}
 
@@ -243,7 +243,7 @@ public void deleteAll(PersistentPropertyPath<RelationalPersistentProperty> prope
 	public <T> void acquireLockById(Object id, LockMode lockMode, Class<T> domainType) {
 
 		String acquireLockByIdSql = sql(domainType).getAcquireLockById(lockMode);
-		SqlIdentifierParameterSource parameter = sqlParametersFactory.forQueryById(id, domainType, ID_SQL_PARAMETER);
+		SqlIdentifierParameterSource parameter = sqlParametersFactory.forQueryById(id, domainType);
 
 		operations.query(acquireLockByIdSql, parameter, ResultSet::next);
 	}
@@ -269,7 +269,7 @@ public long count(Class<?> domainType) {
 	public <T> T findById(Object id, Class<T> domainType) {
 
 		String findOneSql = sql(domainType).getFindOne();
-		SqlIdentifierParameterSource parameter = sqlParametersFactory.forQueryById(id, domainType, ID_SQL_PARAMETER);
+		SqlIdentifierParameterSource parameter = sqlParametersFactory.forQueryById(id, domainType);
 
 		try {
 			return operations.queryForObject(findOneSql, parameter, getEntityRowMapper(domainType));
@@ -355,7 +355,7 @@ public Object mapRow(ResultSet rs, int rowNum) throws SQLException {
 	public <T> boolean existsById(Object id, Class<T> domainType) {
 
 		String existsSql = sql(domainType).getExists();
-		SqlParameterSource parameter = sqlParametersFactory.forQueryById(id, domainType, ID_SQL_PARAMETER);
+		SqlParameterSource parameter = sqlParametersFactory.forQueryById(id, domainType);
 
 		Boolean result = operations.queryForObject(existsSql, parameter, Boolean.class);
 		Assert.state(result != null, "The result of an exists query must not be null");